1. Field of the Invention
The present invention relates to a control system for deployment of an air bag situated in a vehicle, and, more particularly, to an apparatus and method for controlling deployment of the air bag under various collision conditions.
2. Description of the Related Art
Vehicles are now being provided with one or more air bags to provide protection to a passenger in the event of certain vehicle collisions. In fact, the employment of an air bag in vehicles is becoming mandatory in some countries. Accompanying such an air bag is a deployment control system for controllably deploying the air bag under only appropriate circumstances. For example, an air bag should be deployed when the front of the vehicle impacts an obstruction at a sufficient speed, such as 30 mph, or when the vehicle impacts a pole-like obstruction at a sufficient speed. However, an air bag should not be deployed if the vehicle is simply operating on a rough road or is slowly running over the top of a small obstruction, such as a curb.
To distinguish between various types of collisions, air bag deployment control systems, such as the control disclosed in U.S. Pat. No. 5,067,745, analyze deceleration data collected from an accelerometer disposed at some location in the front of the vehicle. Other controls, such as that disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 55-19627, use an array of sensors disposed in the front of the vehicle. Because it is difficult, if not impossible, to timely distinguish a slight collision, i.e., one not requiring deployment, from a serious collision, i.e., one requiring deployment, from solely an analysis of the speed change values (velocity) collected from the accelerometer, various methods of analysis have developed in the prior art.
Considering the various methods of analysis employed in air bag deployment control, in U.S. Pat. No. 5,067,745, the deceleration signal detected by the accelerometer is decomposed through filtering and then the low-frequency components of the deceleration detection signal are combined with the high frequency components and then compared to a predetermined constant value at a particular critical point in time to determine whether a serious collision has occurred. In other systems, such as the system discussed in association with FIG. 2 herein, the velocity, energy, and oscillation is calculated from the deceleration signal and compared to respective calibrated, time-dependent boundary curves for velocity, energy and oscillation. In general, when the quantity calculated at any point in time exceeds the applicable boundary curve at that point in time, the air bag is deployed.
The calculations required by the analysis employed must be accomplished in a short amount of time, such as 30 milliseconds, which is shorter in the severe collision and longer in the slight collision. This critical time is determined by the need to deploy the air bag in an expedient manner to adequately protect the occupant of the vehicle. Furthermore, controls which compare the computed velocity, energy and oscillation to time-dependent boundary curves require complex calculations. Therefore, it is desired to provide an air bag deployment control system which minimizes the amount and complexity of calculations necessary to ascertain whether the air bag should be deployed.
In systems which utilize time-dependent boundary curves for comparison to computed time-dependent values, the time-dependency of the boundary curves necessitates a level of accuracy which often requires numerous crash tests under each of a variety of collision conditions to be performed to obtain the time-dependent boundary curves. It is preferable to reduce the number of crash tests required to determine the proper comparison data.
Also, when employing boundary curves in the analysis performed by the control, significantly more memory is required for storage of the boundary curve(s) than is necessary when utilizing a constant threshold for comparison purposes. The requirement for additional memory increases the cost of the control system. It is therefore desired to provide an effective air bag deployment control system which does not utilize time-dependent boundary curve(s) for comparison purposes to thereby reduce the costs of such a control by minimizing the control's memory requirements.
As previously noted, some control systems, such as that disclosed in U.S. Pat. No. 5,067,745, utilize particular frequency components of the deceleration signal for its analysis. This results in additional manufacturing costs as a filter is required to separate the frequency components of the deceleration signal. It is desired to develop an air bag deployment control system which does not require a special filter to thereby reduce manufacturing costs.
In general, the air bag deployment control systems of the prior art utilize various combinations of calculated values of velocity, energy, and oscillation to determine whether or not the air bag should be deployed. In using these values, there still exists the potential for having difficulty in distinguishing a low-speed, frontal barrier collision in which the air bag is not to be deployed from a higher speed, pole impact collision in which the air bag is to be deployed. Therefore, it is desired to provide an air bag deployment control system which utilizes a function calculated from the deceleration data collected which more effectively distinguishes the low-speed, frontal barrier collision from a higher speed, pole impact collision.